Specific aims of this study include: (1) etiological, epidemiological, clinical, immunological, and pathogenetic characterization of spontaneous yersiniosis, arthritis and amyloidosis in nonhuman primates, (2) isolation and characterization of nonhuman primate amyloid and the acute phase serum protein (SAA) that is though to be the precursor of tissue amyloid, (3) evaluation of the response of nonhuman primates to challenge with either Yersinia organisms or its endotoxin, particularly with reference to SAA response and subsequent development of reactive arthritis and/or amyloidosis, (4) evaluation of various treatment regimens in both spontaneous and experimentally induced cases of amyloidosis and reactive arthritis, and (5) documentation of the histocompatibility antigen make-up of the rhesus monkey population housed in this environment to determine if specific RhLA show increased susceptibility to these diseases as has been documented in the human population for certain HLA types. Yersiniosis, reactive arthritis and anyloidosis occur with considerable frequency in the human population and there are no animal models for reactive arthritis, and no nonhuman primate models for amyloidosis. Reactive arthritis in humans is generally an acute arthritis, but it can become chronic and disabling. The high risk group for development of this type of arthritis is young adult males and thus, a study of this form of arthritis will have some military relevance. Amyloidosis is a progressive, fatal disease with no effective methods for prevention or treatment. The ultimate goal of these studies is to develop a model for these common human diseases in an animal species that is phylogenetically close to man. Such studies should provide data that are directly applicable to the pathogenesis and treatment of these diseases in man. The histocompatibility antigen studies have the potential to significantly contribute to the understanding of genetic susceptibility to disease.